1. Field of the Invention
This invention relates to digital switch assemblies, and more particularly to switch assemblies capable of assembly by modules from the front of an instrument panel for providing a highly visible numerical display of switch circuits selected.
2. Description of the Prior Art
At least since 1959, the digital switch has been known to provide a convenient man to machine interface for digital equipment. Circuit assemblies are constructed capable of performing a selection of many different functions. The selection is frequently made by a rotary element type switch. The multiple leads of the switch are connected into the various circuit assemblies. Frequently, the circuit assemblies and switch arrangement are mounted in an enclosure having a front panel.
The switch rotary elements, when turned, selects various of the circuits in the assembly, according to circuit design. Frequently the rotary element is turned by the thumb, thus acquiring the name "thumbwheel" switch. Other switches utilize levers or push button operated ratchet mechanisms. Hereinafter in this description, the term "thumbwheel" will be used to describe a rotatable element having detents suitable for contact by a thumb or finger for rotation, and where clearly not contradictory, may include lever operated and push button rotary switch assemblies as well.
The thumbwheel usually has some means of providing multiple contacts to an adjacent printed circuit or wire board. The contacts frequently are brushes attached to a common, electrically conductive base so that when any two of the brushes contact separate conductive elements on the printed circuit board, the separate conductive elements are brought into common circuit. The terms "contact" and "brush" are frequently used interchangeably to denote the electrically conductive extensions from a common base in the brush set.
The rotating actuator and dial or thumbwheel, brush sets and printed circuit board are frequently constructed as a unit or module. It has been known in the past to construct such modules so that they can be combined in a series of such switches to form an assembly. Frequently, the module has end brackets and assembly straps or studs for interconnection with each other in a series. The assembly itself, further, might have special end units having special end brackets and assembly strips or studs for holding the modules in a pre-selected series order and for holding the assembly within the panel.
In the past, the switch modules frequently provide visible indicators so that one looking at the front of the panel or of the switch module assembly can instantly determine the rotary position of the switch thumbwheel. The indicators frequently are colored to contrast with the switch module and assembly so that they can be discerned with normal ambient light. With time and frequent rubbing with the fingers or thumb, the coloring is worn or discolored so that determining the rotary thumbwheel position is made difficult. Yet other applications are in dark environments where a contrast in coloring is insufficient to give the viewer an indication of the thumbwheel rotary position.
Such module assemblies frequently have a stationary face which is visible from the front of the panel into which the assembly might be constructed. The construction of such assemblies is divisible into two types, a rear mounted switch assembly and a front mounted switch assembly.
In the rear mounted type switch assembly, the series of modules are combined initially. Usually separate end units are attached to the ends of the module series to provide the necessary end brackets. The end brackets may be formed with holes through which screws or studs can be inserted to hold the assembly to the panel. It is usual to provide a hole in the panel into which the rear mounted switch can be inserted. This hole then must be "finished" in some aesthetically acceptable manner.
The fastening element is inserted through the holes in the end brackets and into additional fastening holes provided in the panel. Frequently, these holes in the panel extend through the panel so that some threaded fastening element, such as a nut or screw head is left protruding through the face of the panel.
Rear mounted type switch assemblies have been found desirable in situations where it is important to wire the switch modules to the circuits prior to the final mounting in the housing itself. It is frequently desired in such circumstances to test the switch assembly formed by the combined modules before the front panel is permanently attached to form the finished instrument product. The panel must be carefully attached, however, in order to have the switch assembly protrude through the desired finished opening or hole. The use of threaded fasteners for mounting the switch assembly to the panel is frequently called "hard mounting" the assembly.
The front mounted type switch assembly is used in situations where the panel is already fastened to the housing containing the circuit assemblies. The switch modules are assembled in a series, and as in the rear mounted assemblies, end brackets are combined on both ends of the module series to form the assembly. Thus the switch assembly includes a front face usually comprising a flange extending from the front of the assembly. The flange usually extends over a greater area than than of the hole in the panel, eliminating the requirement for "hole finishing".
The switch modules and the end brackets are frequently provided with tangs or similar type clamping arrangements. The switch assembly, then, can be inserted through the panel hole or opening. The tangs or similar type resilient clamping arrangements, clamp behind the panel to hold the assembly securely to the panel. The clamping arrangement usually obviates the need for unsightly screw holes and threaded fastening element protrusions forward of the panel itself. The use of resilient clamping arrangements is sometimes called "snap-in mounting".
Problems are frequently encountered using the front mounted type switch assembly. In particular, it may be appreciated that it is necessary to install the switch module into the panel itself before the circuit assemblies housed by the panel are connected with the switches. Preliminary testing may require that the modules must be reassembled in a different sequence. In the front mounted type switch assembly, therefore, the assembly must be removed from its permanent attachment to the panel for the necessary rearrangement.
Various arrangements of contact brush sets have been provided to secure the sets to the wheel. For example, some wheels are formed having studs over which the set, having matching holes, is fitted. The studs may be bradded or melted to secure the set. Such sets are attached to the wheel in a relatively permanent way.
Other systems include wheel face slots having simple extensions of the set inserted therein. In this regard, attention is directed to U.S. Pat. No. 3,466,407 issued to Will. Such a set can be removed, perhaps too easily, from the wheel in some circumstances.
It has long been sought to provide indicating arrangements associated with such rotary thumbwheel switch arrangements that will provide a back illuminated switch indicator, which might be viewed clearly in dark environments and after repeated rubbing with fingers and thumbs. Brush set attaching arrangements connecting the set to the wheel in a reliable but replaceable fashion is also desired.
It has also long been sought to provide a rotary switch assembly capable of modular construction and insertion into a panel from either side of the panel, prior to the permanent fixing of an escutcheon or other finishing plate or bezel to conceal an unfinished opening or hole.